1. Field of the Invention
The present invention relates to a phosphorus-containing phenolic resin-based curing agent and a process for producing the same, and more particularly, the phenolic-type phosphorous curing agent has a high molecular weight, and is halogen-free and nonflammable, and features a high glass transition temperature. The curing agent is also a halogen-free, nonflammable resin curing agent suitable for use in making PCB's insulating layer or semiconductor packaging.
2. Description of Related Art
In recent years, electronic industry has been grown rapidly, and the trend for electronic devices is toward high frequency, high speed and versatility. For meeting this trend, the design of substrates for electronic devices has to minimize line width and insulating layer thickness. As insulating layers become thinner and thinner, for maintaining the quality necessary for electronic devices, the substrate of insulating layers has to meet certain requirements, such as low dielectric coefficient, low dissipation factor, high glass transition temperature (abbreviated as Tg), high heat tolerance and flame retardance.
Particularly, for environmental protection and life safety, flame retardance is becoming a common requirement for all electronic materials. The current approach to endowing electronic materials with flame retardance is mainly involved in adding nonflammable curing agents. The existing nonflammable curing agents can be divided into additive nonflammable curing agents and reactive nonflammable curing agents. The former ones are added through physical manners, such as being mixed or dispersed in the target polymer to provide flame retardance. A reactive nonflammable curing agent is used chemically to have its specific functional group reacted with the target polymer and then to combine with the polymer and provide flame retardance thereof.
The existing reactive nonflammable curing agents are typically halogen-containing nonflammable resin. For example, in order to make FR4 for PCB that meets the UL94-VO flammability standard, tetrabromobisphenol-A (TBBP-A) is used as a curing agent to perform curing reaction with epoxy resin and then to endow the resultant laminate substrate with flame retardance. However, the TBBP-A is a halogen-containing flame retardant, and burning waste circuit boards and packaging materials made thereof can generate irritant, corrosive gas such as benzofuran and dioxin that cause pollution to the environment and are harmful to humans. One solution for the pollution problem is to use smoke suppressants. However, smoke suppressants may degrade the mechanical properties of the resultant laminate substrates and lead to photolysis of the resultant packaging materials. Meanwhile, smoke suppressants are migratory and volatile in the resultant materials, being unfavorable to the materials in terms of physical properties and flame retardance.
Another type of flame retardants is organic bromine compounds. However, these compounds are also considered to be environmentally pollutant and toxic and not popular on the market. By comparison, organic phosphorus compound-based flame retardants are unlikely to show the aforementioned disadvantages, and thereby the market demand thereof is growing stably. In addition, the advantages of phosphorous-containing flame retardants include low toxicity, good processability, less adding quantity, less smoke development and good compatibility with resin.
Therefore, in recent years, the technical development, researches and inventions of nonflammable curing agents have been focused on phosphorous-containing nonflammable materials. For instance, U.S. Pat. No. 8,124,716 and U.S. Pat. No. 8,143,357 disclose phosphorous-containing compounds to be used as curing agents for epoxy resin to endow the resultant laminate substrates with excellent mechanical properties, high glass transition temperature (Tg), good flame retardance and good thermal stability. Nevertheless, the curing agents of the prior patents involve complicated synthesis processes, have less structural flexibility, and are less manageable in terms of molecular weight, thus being less suitable for PCB applications where high glass transition temperature (Tg) is required.